Nox isn't linting tests

[theacodes]

Our nox configuration is skipping flake8 linting of tests, we should fix that. :)

[tseaver]

@jonparrott Is this really either "P1" or a bug?

[theacodes]

I'm gonna drop it to a p2 but this is definitely a bug.

[chemelnucfin]

also refer to #3418 which I will close

[dhermes]

@chemelnucfin Note that #3418 also says pylint should be turned back on (it is on, but doesn't cause test failures).